This invention relates generally to multilayer films containing materials that improve surface properties by inclusion of specific additives. More specifically this invention is directed to multilayer films with one or more non-additive containing skin layer or layers covering one or more layers containing anti-block additives.
Anti-blocks are often added to polymeric films to reduce or eliminate blocking or in some instances to reduce the coefficient of friction (COF) in a film. In multilayer films, both organic and inorganic anti-blocks are often located in an outer most layer or layers outside of the multilayer film. Such a location can lead to bleed-out or plate-out during film manufacture, converting of the film to its use, and in its use, such as in a package. The anti-block can also fallout or be broken out of the surface, leading to an undesirable heightening of the COF.
Plate-out on equipment can mean expensive downtime for equipment.
Such anti-blocks can also damage a coated or metallized film surface.
All these tendencies act to keep anti-blocks at a lower level of inclusion and therefore efficacy, than might otherwise be desirable.
U.S. Pat. No. 6,087,015 suggests a matte surface film comprising a) a core layer of thermoplastic polymer, b) matte surface layer which includes a blend of film forming polymers and a polydialkylsiloxane. The film is purported to produce a film having a matte surface layer which has a low coefficient of friction. There is no disclosure to a skin layer over the layer containing the polydialkylsiloxane.
Japanese Patent Application Publication No. 2668799 suggests a biaxially drawn multiple layer film characterized in that a surface layer of a composition comprised of components A and B are laminated on at least one surface of a biaxially drawn crystalline propylene polymer base layer. Component A is 100 parts by weight of at least one resin selected from a propylene-ethylene random copolymer of an ethylene content of 3 to 8 weight percent and a propylene-ethylene-butene-1 random copolymer of an ethylene content of 0.5 to 5 weight percent and a butene-1 content of 3 to 25 weight percent. Component B is 0.1 to 1.0 parts by weight of polydiorganosiloxane of a degree of polymerization n of 3500 to 8000. The film purportedly has markedly improved adaptability to packaging machines and suitability for high speed automatic packaging equipment.
There is a commercial need therefore, for a multilayer film which will reduce or eliminate the issues discussed above relating to an anti-block in an outermost layer or surface of a multilayer film.
We have discovered that a skin layer or layers coextruded over a layer containing organic or inorganic anti-block, can provide a multilayer film having a low COF and a substantial absence of bleed-out, plate-out, scratching another film surface and the like.
A film, comprising a core layer having a first surface and a second surface, the core layer being selected from one of, high density polyethylene (HDPE), linear low density polyethylene (LLDPE), ethylene propylene random copolymer (RCP), isotactic polypropylene homopolymer (iPP), syndiotactic polypropylene (sPP) or combinations thereof, is contemplated. The core layer may be present in the total film at a thickness in the range of from 5-500 xcexcm. Additionally, at least a first tie layer, contiguous to the first surface of the core layer, the first tie layer being one of iPP, RCP, propylene butene copolymer (PB), ethylene propylene butene terpolymer (EPB), HDPE, LLDPE, medium density polyethylene (MDPE), maleic anhydride grafted polypropylene, maleic anhydride grated polyethylene, sPP, or combinations thereof, where the first tie layer further includes in the range of from 0.05-2 weight % of an additive selected from one of amorphous silica, calcium carbonate, magnesium silicate, aluminum silicate, calcium phosphate, crosslinked polymethacrylate, polymethyl silsesquioxane, polycarbonate, polyamide, polyester, polytetrafluoroethylene (PTFE) powder or combinations thereof, the weight % based on the total weight of the first tie layer, wherein the first tie layer has a thickness in the film in the range of from 0.5-10 xcexcm, wherein the additive has a mean particle size in the range of from 0.5-20 xcexcm, and a mean particle size of  greater than 10% of the thickness of the first tie layer; and at least a first skin layer contiguous to the first tie layer, such that the first tie layer is spaced between the core and the first skin layer, the first skin layer being a material selected from one of iPP, RCP, PB, EPB, HDPE, LLDPE, MDPE, ethylene vinyl alcohol (EVOH), EVA copolymer, low density polyethylene (LDPE), ethylene propylene block copolymer or combinations thereof. The skin layer may be substantially free of the additive, wherein the first skin layer has a thickness in the range of from 0.1-8 xcexcm; and the film has a COF, as determined by ASTM D 1894,  less than 2.
These and other features, aspects and advantages of embodiments of our invention, will become better understood with reference to the following description and appended claims.